A stem system for use in total ankle replacement surgery and methods of using the same

Abstract

A stem system for a total ankle replacement implant is provided. The stem system may include an outer shell defining a cavity therein and an inner core configured to be received within the cavity of the outer shell. Each of the outer shell and the inner core may have a plurality of segments, with each adjacent pair of segments being connected by a flexible joint. The flexible joints of the outer shell and inner core may be vertically offset about the longitudinal axis of the stem system, such that when the inner core is disposed within the cavity of the outer shell, the stem system is rigidized.

Description

A STEM SYSTEM FOR USE IN TOTAL ANKLE REPLACEMENT SURGERY AND METHODS OF USING THE SAMECROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 689,179, filed on August 30, 2024, which is hereby incorporated by reference herein in its entirety.FIELD

[0002] This disclosure relates to an ankle prosthesis device. More specifically, this disclosure relates to an ankle prosthesis device having a flexible stem system for facilitating implantation thereof into a cavity within the intramedullary canal of a patient’s tibia.BACKGROUND

[0003] Total ankle replacement is a procedure that is used for patients with, for example, osteoarthritis, post-traumatic arthritis, or rheumatoid arthritis affecting the ankle joint. Depending on the implant and geometries of the tibia, a cavity is drilled to provide space for an ankle prosthesis to be implanted. In some embodiments, the cavity is prepared along the anatomical axis of the tibia to allow for insertion of the prosthesis in the tibial canal.

[0004] Current stems used in total ankle replacements face several challenges, including potential issues with implant stability and integration. One challenge is the risk of a prosthesis loosening after insertion into the patient, which may occur if the stem does not achieve optimal bone integration. Loosening of the prosthesis may lead to complications and the need for one or more additional invasive surgeries. Additionally, stems may not always accommodate the anatomical variations of different patients, resulting in improper fit or alignment of the implant. In some cases, the mechanical properties of the stem, such as its ability to withstand dynamic forces of the ankle joint, may not be ideal, leading to issues like stress shielding or premature wear. It is desirable to provide a stem that achieves optimal bone integration, flexibly adjusts to accommodate anatomical variations of patients, withstands the dynamic forces of the ankle joint, and allows for minimally-invasive insertion from a strategic location of the patient.153545767.2

[0005] Many current stems for total ankle replacement procedures are also straight and inflexible and typically require insertion through an incision on the bottom of a patient’s foot. These implantation methods are highly invasive and may cause unnecessary trauma to the patient, which not only increases recovery time but may also damage or modify non-diseased anatomy in such a way that may temporarily or permanently hinder the patient’s quality of life.

[0006] While some total ankle replacement implants have modular stems that are assembled within the patient’s tibia during insertion, these procedures are very complex and time consuming as they require assembling the stem within the patient’s tibia during the procedure.

[0007] It is therefore desirable to provide an improved stem system for an ankle prothesis to facilitate less invasive ankle replacement surgical procedures.SUMMARY

[0008] In aspects, a stem system for an ankle replacement implant is provided. The stem system may include an outer shell comprising one or more shell joints and an inner core comprising one or more core joints, where the inner core is configured to be received within a cavity defined within the outer shell, and where when the inner core is disposed with in the outer core, the shell joints and the core joints are vertically offset about a longitudinal axis of the stem system.

[0009] In some aspects, the outer shell includes a plurality of shell segments, where each of the one or more shell joints is disposed between each adjacent pair of shell segments. In some aspects, each of the one or more shell joints are ball-in-socket joints.

[0010] The one or more shell joints may be configured to bend with a limited range of motion in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint. In some aspects, the outer shell has three shell segments and two shell joints.

[0011] In some aspects, the inner core includes a plurality of core segments, wherein each of the one or more core joints is disposed between each adjacent pair of shell segments. In some aspects, each of the one or more core joints are ball-in-socket joints. The one or more core joints may be configured to bend with a limited range of motion in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint. In some aspects, the inner core has three core segments and two core joints. In some aspects, the inner core is secured within the253545767.2cavity of the outer shell using a friction fit, a press fit, or a tapered fit. Tn some aspects, the offset between the shell joints and the core joints is effective to rigidize the stem system.

[0012] In another aspect, an ankle replacement implant is provided. The ankle replacement implant may include a stem system having an outer shell comprising a plurality of shell segments and one or more shell joints disposed between each adjacent pair of shell segments, and an inner core comprising a plurality of core segments and one or more core joints disposed between each adjacent pair of core segments. The inner core may be configured to be received within a cavity of the outer shell, and when the inner core disposed within the cavity of the outer shell, the stem system may be rigidized.

[0013] In some aspects, the ankle replacement implant also includes a tibial tray. The tibial tray may include a mating protrusion extending from a top surface thereof, the mating protrusion being configured to attach the tibial tray to the stem system. The mating protrusion may be received within the cavity of the outer shell and is configured to attach the tibial tray to the outer shell using a friction fit, a press fit, or a tapered fit.

[0014] In some aspects, each of the one or more shell joints are ball-in-socket joints. The one or more shell joints may be configured to bend with a limited range of motion in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint. In some aspects, the outer shell has three shell segments and two shell joints.

[0015] In some aspects, each of the one or more core joints are ball-in-socket joints. The one or more core joints may be configured to bend with a limited range of motion in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint. In some aspects, the inner core comprises three core segments and two core joints. In some aspects, the inner core is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit. When the inner core is disposed with in the outer core, the shell joints and the core joints may be vertically offset about a longitudinal axis of the stem system, the vertical offset between the shell joints and the core joints being effective to rigidize the stem system.

[0016] In yet another aspect, a method of implanting a stem system for total ankle replacement implant is provided. The method includes inserting an outer shell into a tibial canal of a patient and inserting an inner core into a cavity defined within the outer shell. The stem system may have a unitary construction when the inner core is inserted into the cavity of the353545767.2outer shell, and each of the outer shell and the inner core may be flexible, but the stem system may become rigid when the inner core is inserted into the cavity of the outer shell.

[0017] In some aspects, the outer shell includes a plurality of shell segments and one or more shell joints connecting each adjacent pair of shell segments. The plurality of shell segments and the one or more shell joints may enable the flexibility of the outer shell. The outer shell may be configured to bend at each of the one or more shell joints with a limited range of motion and in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint.

[0018] In some aspects, the inner core includes a plurality of core segments and one or more core joints connecting each adjacent pair of core segments. The plurality of core segments and the one or more core joints may enable the flexibility of the inner core. The inner core may be configured to bend at each of the one or more core joints with a limited range of motion and in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint.

[0019] In some aspects, the outer shell includes one or more shell joints and the inner core includes one or more core joints, and wherein when the inner core is disposed with in the outer core, the shell joints and the core joints are vertically offset about a longitudinal axis of the stem system, the vertical offset between the shell joints and the core joints being effective to rigidize the stem system. In some aspects, the inner core is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.

[0020] In some aspects, the method also includes attaching a tibial tray to the stem system. The tibial tray may have a mating protrusion configured to be received within the cavity of the outer shell. The mating protrusion may be secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The detailed description is set forth with reference to the accompanying drawings. The use of the same reference numerals may indicate similar or identical items. Various embodiments may utilize elements and / or components other than those illustrated in the drawings, and some elements and / or components may not be present in various embodiments. Elements and / or components in the figures are not necessarily drawn to scale. Throughout this disclosure, depending on the context, singular or plural terminology may be used interchangeably.453545767.2

[0022] FIG. 1 is a side view of a portion of a total ankle replacement implant having a flexible stem system, according to one or more embodiments of the present disclosure.

[0023] FIG. 2 is a cross-sectional view of the total ankle replacement implant of FIG. 1, according to one or more embodiments of the present disclosure.

[0024] FIG. 3A is a perspective view of an outer shell for a flexible stem system of a total ankle replacement implant, according to one or more embodiments of the present disclosure.

[0025] FIG. 3B is an exploded view of the outer shell of FIG. 3 A, according to one or more embodiments of the present disclosure.

[0026] FIG. 4A is a perspective view of an inner core for a flexible stem system of a total ankle replacement implant, according to one or more embodiments of the present disclosure.

[0027] FIG. 4B is an exploded view of the inner core of FIG. 4A, according to one or more embodiments of the present disclosure.

[0028] FIG. 5 is a flow diagram of a method for inserting a flexible stem system for a total ankle replacement implant into a tibia of a patient, according to one or more embodiments of the present disclosure.

[0029] FIGS. 6A-6E depict a schematic of the method of FIG. 4, according to one or more embodiments of the present disclosure.

[0030] FIG. 7 is a perspective view of the total ankle replacement implant of FIGS. 1-2 inserted within a tibia of a patient, according to one or more embodiments of the present disclosure.DETAILED DESCRIPTION

[0031] The disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0032] Certain terminology is used in the following description for convenience only and is not limiting. The words “front,” “upper,” and “lower” designate directions in the drawings to which reference is made.

[0033] The coronal, sagittal, and axial planes are also referenced throughout this disclosure. These directional terms are used according to their generally accepted definitions as used in the553545767.2medical field unless explicitly clarified herein. The terms superior / inferior, medial / lateral, posterior / anterior, and distal / proximal are similarly used according to the generally accepted definitions as used in the medical field, unless explicitly clarified herein. The drawings may include further clarifications regarding these directions and planes to the extent it is believed necessary. The terms top / bottom are sometimes used interchangeably with superior / inferior, and the term side is sometimes used interchangeably with medial / lateral.

[0034] A flexible stem system for a total ankle replacement implant is described herein. The stem system may include multiple segments that at least partially pivot relative to one another in order to provide enhanced flexibility and adaptability, improved load distribution, and for facilitating the surgical placement of the stem. The multi segmented structure of the stem enables the stem to “turn a corner,” allowing for insertion from a posterior position, for example, instead of through the patient’s calcaneus and / or talus. The multi segmented, flexible structure of the stem may also improve load distribution by allowing for slight adjustments in the alignment of the stem to evenly distribute load across the bone, and may also facilitate surgical placement of the stem by improving a surgeon’s ability to position and align the stem in a manner that minimized bone resection in the patient because the stem may conform to a desired shape that allows for insertion from a desirable angle and location.

[0035] The stem system may be better understood with reference to the accompanying drawings. A portion of a total ankle replacement implant, having a flexible stem system, is shown in FIGS. 1-2.

[0036] In embodiments, the total ankle replacement implant 10 includes a tibial tray 50 and a stem system 100 extending upward therefrom. The tibial tray 50 is located at a distal end 12 of the implant 10, with the stem 100 extending towards a proximal end 14 of the implant 10 from a top side 52 of the tibial tray 50. The bottom side 54 of the tibial tray 50 is designed to sit within the gap between the patient’s tibia and talus, to be attached to one or more articulating surfaces (not shown), after it is implanted. The stem system 100 may be flexible to so that it may be inserted from a posterior position rather than through the patient’s calcaneus and / or talus. In some embodiments, the stem 100 includes an indent 101 on one or more sides thereof near the distal end 12 of the implant 10. The indent 101 may be configured to receive a fixture therein, the fixture being used to aid the surgeon in gripping and holding the stem 100 during the insertion procedure.653545767.2

[0037] The stem system 100 may include an outer shell 102 having one or more shell segments 104 and shell joints 106 connecting each adjacent pair of shell segments 104. In some embodiments, as shown in FIGS. 1-2, the outer shell 102 has three segments 104 and two flexible joints 106. However, the outer shell 102 may have additional or fewer shell segments 104 (and shell joints 106) depending on the desired length (L) of the stem system 100. The outer shell 102 may be configured to bend at each of the shell joints 106 to facilitate insertion of the shell 102 into the patient’s tibia through the space between the tibia and the talus (rather than through the bottom of the patient’s foot. According to preferred embodiments, the shell joints 106 are ball-in-socket joints. For example, the proximal end (e.g., ball end) of each shell segment 104 may be configured to fit into the distal end (e.g., socket end) of an upwardly adjacent segment 104. In some embodiments, the ball is snap fit into the socket. In other embodiments, the ball is moveably secured within the socket using one or more pins, or another like fixation mechanism. The proximal end of the last shell segment may not include a joint. In some embodiments, the shell joints 106 are only capable of bending in a single direction in accordance with the desired angle and direction of insertion. In other embodiments, the shell joints 106 are capable of bending in any direction, such that the shell segments 104 may be capable of freely rotating about the shell joints 106.

[0038] In some embodiments, each shell joint 106 may also include one or more outer passages 103 through which a pin (not shown) or other fixation mechanism may be fitted. The shell joint 106 may also include one or more inner passages (not shown) in the ball portion of the downwardly adjacent segment 104 that may also receive the pin, for securing adjacent segments together. The pin may help to secure the joint 106 while still permitting the joint 106 to bend as needed to facilitate insertion of the shell 102 into the patient’s tibial canal. A pin may be placed on one or both sides of the joint 106, but should not pass through the cavity 114.

[0039] In embodiments, the outer shell 102 is sized and shaped to fit within a canal formed within a patient’s tibia for receiving the stem 100 of the implant 10 therein. As the outer shell 102 is advanced into the tibial canal, the outer shell 102 substantially straightens and conforms to the shape of the tibial canal. Once the outer shell 102 is fully inserted into the patient’s tibial canal, the outer shell 102 will adopt the straight (or substantially straight) configuration shown in FIG. 1.753545767.2

[0040] As shown in FIG. 2, the stem system 100 also includes an inner core 108 that, like the outer shell 102, has one or more core segments 110 and a core joint 112 connecting each adjacent pair of core segments 110. In some embodiments, the inner core 108 has three core segments 110 and two core joints 112. However, the inner core 108 may have additional or fewer core segments 110 (and core joints 112) depending on the desired length (L) of the stem system 100. According to preferred embodiments, the outer shell 102 and inner core 108 each have the same number of segments 104, 110 and joints 106, 112. However, it is also possible that the outer shell 102 and inner core 108 have a different number of segments 104, 110 and joints 106, 112.

[0041] In embodiments, the inner core 108 is sized and shaped to fit within a cavity 114 defined within the outer shell 102. The inner core 108 may therefore be configured to bend at each of the core joints 112 to facilitate insertion of the core 108 into the cavity 114 of the outer stem 102, once the outer stem 102 has been inserted into the patient’s tibia, through the space between the tibia and the talus (rather than through the bottom of the patient’s foot). According to preferred embodiments, the core joints 112 are ball-in-socket joints. In some embodiments, the core joints 112 are only capable of bending in a single direction in accordance with the desired angle and direction of insertion. In these embodiments, the core joints 112 bend at the same angle as the shell joints 104. In other embodiments, the core joints 112 are capable of bending in any direction, such that the core segments 110 may be capable of freely rotating around the core joints 112.

[0042] In some embodiments, each core joint 112 may also include an outer passage 109 through which a pin (not shown) or other fixation mechanism may be fitted. The core joint 112 may also include one or more inner passages (not shown) in the ball portion of the downwardly adjacent segment 110 that may also receive the pin, for securing adjacent segments together. The pin may help to secure the joint 112 while still permitting the joint 112 to bend as needed to facilitate insertion of the core 108 into the cavity 114 of the shell. A pin may be placed on one or more sides of the joint 112, and also may extend through the core 108.

[0043] As the inner core 108 is inserted and advanced into the cavity 114 of the outer shell 102, the inner core 108 straightens and conforms to the shape of the cavity 114. Once the inner core 108 is fully inserted into the cavity 114, the inner core 108 will adopt the straight (or substantially straight) configuration shown in FIG. 2.853545767.2

[0044] In preferred embodiments, the inner core 108 is secured within the outer shell 102 using a friction fit, press fit, or tapered fit. In other embodiments, the inner core 108 is secured within the outer shell 102 using a mechanical interlocking mechanism (e.g., a ridge, a groove, or a key) or an external fixation mechanism (e.g., a locking pin). In some embodiments, the shell 102 includes one or more openings 107 towards the distal end 12 thereof, which may aid the surgeon in confirming that the inner core 108 is properly secured within the outer shell 102. The one or more openings 107 may also be used to release the inner core 108 from its fit within the outer shell 102 if needed.

[0045] In embodiments, the shell joints 106 are vertically offset from the core joints 112, such that when the inner core 108 is inserted into the outer shell 102, the entire stem system 100 (i.e., the outer shell 102 and the inner core 108) are fixed in a straight (or substantially straight) configuration such that neither the outer shell 102 nor the inner core 108 is cable of flexing or bending about the joints 106, 112. More specifically, thejoints 106, 112 are disposed along the longitudinal axis (LA) extending between the proximal end 14 and distal end 12 of the stem 100 when the stem 100 is in the straight (or substantially straight) configuration. The shell joints 106 and the core joints 112 are positioned at different offset points along the longitudinal axis of the stem 100, where this misalignment of thejoints 106, 112 prevents both the shell 102 and the core 108 from bending when the stem 100 is assembled (i.e., when the core 108 is inserted into the cavity 114 of the shell 102.

[0046] Thejoints 106, 112 and offset thereof maintains the rigidity of the assembled stem 100 while also simplifying the manner of insertion and assembly. According to preferred embodiments, thejoints 106, 112 are hinge joints that bend (or hinge) in a single direction (as described in greater detail with respect to FIGS. 3A-4B) to facilitate insertion of each stem 100 component, i.e., the shell 102 and the core 108, into the tibial canal using an anterior approach. By segmenting the shell 102 and the core 108 in this way, thejoints 106, 112 provide sufficient flexibility so as to enable anterior insertion even for a stem 100 having an extended length (i.e., 30 mm or greater). Rigid stems of this length cannot be inserted using an anterior approach, and while shorter stems may be inserted in this manner, these stems are less stable due to the shorter length. Therefore, by providing a stem 100 with a flexible shell 102 and core 108 as described herein, the stem 100 may advantageously have a sufficient length (i.e., greater than 30 mm) to provide better fixation and stability for the total ankle replacement implant 10, while still953545767.2permitting use of a less invasive anterior insertion method typically used for implants having shorter stems.

[0047] When the stem 100 is assembled (i.e., when the core 108 is inserted into the shell 102), the vertical offset of the joints 106, 112 prevents each of the shell 102 and the core 108 from bending or flexing relative to each other when the stem 100 is assembled, and therefore prevents the entire stem 100 from bending within the tibial canal (i.e., the stem 100 remains rigid and stable within the tibia). That is, while the joints 106, 112 are configured to hinge to facilitate insertion into the tibia using an anterior approach, the longitudinal offset of the joints 106, 112 when the stem 100 is assembled prevents the respective joints 106, 112 of each component (i.e., the shell 102 and the core 108) from hinging. For example, the core joints 112 will be prevented from bending because the joints 112 are positioned within a rigid portion of the shell 102 (i.e., not within the shell joints 106) that is incapable of flexing or hinging. Likewise, the shell joints 108 will be preventing from bending because the joints 106 are positioned surrounding a rigid portion of the core 108 (i.e., not surrounding the core joints 112) that is incapable of flexing or hinging.

[0048] In some embodiments, one or both of the outer shell 102 and inner core 108 are provided with an additional fixation mechanism to further secure the outer shell 102 and the inner core 108, and to increase the rigidity of the assembled stem system 100. For example, the shell 102 and core 108 may be configured to receive one or more pins for securing the shell 102 and the core 108 together, preferably towards the distal end 12 of the implant 10. Other fixation mechanisms that may be implemented include but are not limited to screws, rivets or other fasteners, and ball detent mechanisms.

[0049] While the joints 106, 112 are described herein as being ball-in-socket joints, it would be understood that other types of joints may be used. For example, the joints 106, 112 may be a dovetail joint, a spline joint, a press-fit joint, or any other type of joint known in the art. Moreover, as described in greater detail with respect to FIGS. 3A-4B, the joints 106, 112 may be provided with additional fixation means to secure the joints 106, 112 while still permitting the appropriate range of motion of flexibility therein. In the embodiments described with respect to FIGS. 3A-3B, the components of the joints 106, 112 are further secured with one or more pins. However, any fixation means known in the art for securing two or more components while still1053545767.2permitting rotational movement thereof may be used, including but not limited to screws, rivets or other fasteners, and ball detent mechanisms.

[0050] The joints 106, 112, may be another joint type (i.e., not a hinge joint) configured to rotational movement. That is, the joints 106, 112 may be configured for any form rotational movement, such as the hinge joints as previously described. Other joints configured for rotational movement may include, but are not limited to, pivot joints, ellipsoidal joints, saddle joints, pin joints, linear or sliding joints, gliding joints, cylindrical joints, constant velocity joints, and flexure joints. Any suitable joints may be used herein.

[0051] In embodiments, after the inner core 108 is inserted into the outer shell 102, a gap 116 will remain within the cavity 114 towards the distal end 12 of the implant 10. The tibial tray 50 may include a mating protrusion 56 which is sized and shaped to fit within the gap 116 of the cavity 114. The mating protrusion 56 may extend upward from the top side 52 of the tibial tray 50, such that a top end 58 of the mating protrusion 56 resides within the cavity 114. In some embodiments, the top end 58 of the mating protrusion 56 is spaced apart from the inner core 108. In other embodiments, the top end 58 of the mating protrusion 56 abuts the inner core 108.

[0052] In some embodiments, the mating protrusion 56 is secured within the outer shell 102 by a press fit or friction fit. In other embodiments, the mating protrusion 56 is secured within the outer shell using a mechanical interlocking mechanism (e.g., a ridge, a groove, or a key) or an external fixation mechanism (e.g., a locking pin). The insertion of the mating protrusion 56 into the gap 116 may also help to further secure the inner core 108 within the outer shell 102.

[0053] In some embodiments, the inner core 108 may also include a threaded site 118, which may be used for attaching a threaded instrument thereto to facilitate removal of the inner core 108 from the outer shell 102. In other embodiments, the threaded site 118 may be used for connecting the inner core 108 to the mating protrusion 56 of the tibial tray 50.

[0054] Referring now to FIGS. 3A-4B, the outer shell 102 (FIGS. 3A-3B) and inner core 108 (FIGS. 4A-4B) are shown in greater detail. According to preferred embodiments, as shown in FIGS. 3A-3B, the outer shell 102 has three shell segments 104 where each adjacent pair of shell segments 104 is connected by a shell joint 106. However, as discussed with respect to FIGS. 1-2, the outer shell 102 may include more than three or fewer than three shell segments 104 as needed to customize the length (L) of the stem 100 based on patient anatomy.1153545767.2

[0055] The three shell segments 104 may include a top shell segment 104a, a middle shell segment 104b, and a bottom shell segment 104c, where the top shell segment 104a and the middle shell segment 104b are connected by a first shell joint 106a and the middle shell segment 104b and the bottom shell segment 104c are connected by a second shell joint 106b. In some embodiments, such as that shown in FIGS. 3A-3B, each of the top shell segment 104a, middle shell segment 104b, and bottom shell segment 104c are substantially cylindrical. In other embodiments, the shell segments 104 are any other shape suitable for forming a stem 100 for a total ankle replacement implant.

[0056] The top shell segment 104a may be cylindrical (or substantially cylindrical), with the distal end 120a being flat (or substantially flat). In some embodiments, the proximal end 122a of the top shell segment 104a is conical. In other embodiments, the proximal end 122a of the top shell segment 104a may be any other shape suitable for facilitating insertion into the prepared hole within the distal end of the tibia and the tibial canal. The middle shell segment 104b may also be cylindrical (or substantially cylindrical) and has a partially spherical or bulbous protrusion 124b extending from distal end 122b thereof. In some instances, the bulbous protrusion 124b is configured to form a ball- in-socket joint with the upwardly adjacent top shell segment 104a. For example, the bulbous protrusion 124b forms a part of the first shell joint 106a and is configured to be received within a reciprocal cavity 126a (forming the other part of the first shell joint 106a) at the distal end 120a of the top shell segment 104a. In some embodiments, the bulbus protrusion 124b is configured to be snap-fit within the reciprocal cavity 126a. In these embodiments, the reciprocal cavity 126a may have curvature designed or configured to receive the bulbous protrusion 124b so that the two components are able to form a snap-fit.

[0057] In other embodiments, the bulbous protrusion 124b is moveably secured within the reciprocal protrusion 126a using one or more pins, or another like fixation mechanism. The one or more pins may pass through the outer passage 103a at the distal end 120a of the top shell segment 104a and the inner passage 105b defined within the bulbous protrusion 124b at the proximal end 122b of the middle shell segment 104b. The one or more pins may be present in addition to, or in alternative to, the snap-fit of the bulbous protrusion 124b in the reciprocal cavity 126a.

[0058] Similar to the middle shell segment 104b, the bottom shell segment 104c may be cylindrical (or substantially cylindrical) with a partially spherical protrusion or bulbous1253545767.2protrusion 124c extending from the proximal end 122c thereof. Tn some instances, the bulbous protrusion 124c is configured to form a ball-in-socket joint with the upwardly adjacent middle shell segment 104b. For example, the bulbous protrusion 124c forms a part of the second shell joint 106b and is configured to be received within a reciprocal cavity 126b (forming the other part of the second shell joint 106b) at a distal end 120b of the middle shell segment 104b. In some embodiments, the bulbous protrusion 124c is configured to be snap-fit within the reciprocal cavity 126b. In these embodiments, the reciprocal cavity 126b may have a curvature designed or configured to receive bulbous protrusion 124c so that the two components may form a snap-fit.

[0059] In other embodiments, the bulbous protrusion 124c is moveably secured within the reciprocal cavity 126b using one or more pins (not shown), or another like fixation mechanism. The one or more pins may pass through the outer passage 103b at the distal end 120b of the middle shell segment 104b and the inner passage 105c defined within the bulbous protrusion 124c at the proximal end 122c of the bottom shell segment 104c. The one or more pins may be present in addition to, or in the alternative to, the snap-fit of the bulbous protrusion 124c in the reciprocal cavity 126b.

[0060] The distal end 120c of the bottom shell segment 104c may be flat and, when the ankle replacement implant 10 is assembled, is adjacent to the top surface 52 of the tibial tray 50.

[0061] The reciprocal cavities 126a, 126b may be at least partially defined by a cutaway 128a, 128b that, when the partially spherical protrusion 124b, 124c articulates within the cavity 126a, 126b, facilitates bending of the adjacent shell segments 104 relative to one another. For example, the shape, size, and angle of the cutaway may dictate the direction in which the respective joint is able to bend and the extent to which the joint is able to bend.

[0062] In embodiments, first referring to the first joint 106a, the cutaway 128a defines a cutaway surface 129a which extends upwardly at a less than 90° angle from the bottom surface 127a of the distal end 120a of the top shell segment 104a. When the shell 102 is in the straight configuration, as shown in FIG. 3 A, the bottom surface 127a is in a plane perpendicular to the longitudinal axis (LA) of the stem 100 and abuts a top surface 125b at the proximal end 122b of the middle shell segment 104b surrounding the bulbous protrusion 124b. As the first joint 106a bends, the bottom surface 127a of the top shell segment 104a distances from the top surface 125b of the middle shell segment 104b. In the fully bent configuration, such as that shown in FIG. 6 A, the cutaway surface 129a abuts the top surface 125b of the middle shell segment 104b. In this1353545767.2way, the first joint 106a is only permitted to bend in the direction of the cutaway 128a, and the angle of the cutaway 128a relative to the plane perpendicular to the longitudinal axis (LA) of the stem 100 dictates the extent to which the first joint 106a is permitted to bend.

[0063] Similarly, referring now to the second joint 106b, the cutaway 128b defines a cutaway surface 129b which extends upwardly at a less than 90° angle from the bottom surface 127b of the distal end 120b of the middle shell segment 104b. When the shell 100 is in the straight configuration, the bottom surface 127b is in a plane perpendicular to the longitudinal axis (LA) of the stem 100 and abuts a top surface 125 c at the proximal end 122c of the bottom shell segment 104c. As the second joint 106b bends, the bottom surface 127b of the middle shell segment 104b distances from the top surface 125c of the bottom shell segment 104c. In the fully bent configuration, the cutaway surface 129b abuts the top surface 125 c of the bottom shell segment 104c. In this way, the second joint 106b is only permitted to bend in the direction of the cutaway 128b, and the angle of the cutaway 128b relative to the plane perpendicular to the longitudinal axis (LA) of the stem 100 dictates the extent to which the second joint 106b is permitted to bend.

[0064] The cutaways 128a, 128b may be any shape and / or size so as to provide the shell joints 106a, 106b with the appropriate range of motion for the desired bending of the outer shell 102. In preferred embodiments, the cutaways 128a, 128b are positioned so that each joint 106a, 106b is only able to bend in one direction and to a degree that is preferred for insertion of the outer shell 102 along the sagittal plane. In this preferred embodiment, the cutaways 128a, 128b are aligned on a single side of the outer shell 102 so that each shell joint 106a, 106b bends in the same direction. In other embodiments, the cutaways 128a, 128b may be positioned so that the joints 106a, 106b can bend in multiple directions. In these other embodiments, the cutaways 128a, 128b may not be aligned on a single side of the shell 102, thereby enabling the shell 102 to bend in a different direction at each joint 106.

[0065] The shell segments 104, when assembled to form the shell 102, define a cavity 114 for receiving the core 108 therein. Each shell segment 104 may include openings at the proximal and / or distal ends thereof for facilitating passage of the core 108 through the cavity. For example, beginning at the distal end 12 of the shell 102, the bottom shell segment 104c includes an inlet 121c at the distal end 120c thereof for initially receiving the core 108, and an outlet 123c through the bulbous protrusion 124c at the proximal end 122c thereof through which the core1453545767.2108 will pass after traversing through the bottom shell segment 104c. The core 108 will then enter the middle shell segment 104b through an inlet 121b at the distal end 120b of the middle shell segment 104b and exit through the outlet 123b in the bulbous protrusion 124b of the middle shell segment 104b at its proximal end 122b. The core 108 may then enter the top shell segment 104a through the inlet 121a at the distal end 120a thereof. The cavity 114 terminates within the top shell segment 104a (i.e., the top shell segment 104a does not have an outlet).

[0066] In preferred embodiments, as shown in FIGS. 4A-4b, the inner core 108 (like the outer shell 102 of FIGS. 3A-3B) also has three core shell segments 110 where each adjacent pair of core segments 110 is connected by a core joint 112. As with the outer shell 102, the inner core 108 may include more than three or fewer than three core segments 110 as needed to customize the length (L) of the stem 100 as needed.

[0067] The three core segments 110 may include a top core segment 110a, a middle core segment 110b, and a bottom core segment 110c, where the top core segment 110a and the middle core segment 110b are connected by a first core joint 112a and the middle core segment 112b and the bottom core segment 112c are connected by a second shell joint 106b. In some embodiments, such as that shown in FIGS. 4A-4B, each of the top core segment 110a, middle core segment 110b, and bottom core segment 110c are substantially cylindrical. In other embodiments, the shell segments 104 are any other shape suitable for forming a stem 100 for a total ankle replacement implant.

[0068] The top core segment 110a may be cylindrical (or substantially cylindrical), with the distal end 130a being flat (or substantially flat). In some embodiments, the proximal end 132a of the top (most proximal) core segment 110a is conical. In other embodiments, the proximal end 132a of the top core segment 110a may be any other shape suitable for facilitating insertion into the prepared hole within the distal end of the tibia and the tibial canal. The middle core segment 110b may also be cylindrical (or substantially cylindrical) and has a spherical protrusion 134b extending from the distal end 132b thereof. In some instances, the spherical protrusion 134b is configured to form a ball-in-socket joint with the upwardly adjacent top core segment 108a. For example, the spherical protrusion 134b forms a part of the first core joint 112a and is configured to be received within a reciprocal cavity 136a (forming the other part of the first core joint 112a) at the distal end 130a of the top core segment 110a. In some embodiments, the spherical protrusion 134b is configured to be snap-fit within the reciprocal cavity 136a. In these1553545767.2embodiments, the reciprocal cavity 136a may have curvature designed or configured to receive spherical protrusion 136a so that the two components may form a snap-fit.

[0069] In other embodiments, the spherical protrusion 134b is moveably secured within the reciprocal protrusion 136a using one or more pins, or another like fixation mechanism. The one or more pins may pass through the outer passage 109a at the distal end 130a of the top core segment 1101 and the inner passage 111b defined within the spherical protrusion 134b at the proximal end 132b of the middle core segment 104b. The one or more pins may be present in addition to, or in alternative to, the snap-fit of the spherical protrusion 134b in the reciprocal cavity 136a.

[0070] Similar to the middle core segment 110b, the bottom core segment 110c may be cylindrical (or substantially cylindrical) with a spherical protrusion 134c extending from the proximal end 132c thereof. In some instances, the spherical protrusion 134c is configured to form a ball-in-socket joint with the upwardly adjacent middle core segment 110b. For example, the spherical protrusion 134c forms a part of the second core joint 112b and is configured to be received within a reciprocal cavity 136b (forming the other part of the second core joint 112b) at a distal end 130b of the middle core segment 110b. In some embodiments, the spherical protrusion 134c is configured to be snap-fit within the reciprocal cavity 136b. In these embodiments, the reciprocal cavity 136b has a curvature designed or configured to receive the spherical protrusion 136c so that the two components may form a snap-fit.

[0071] In other embodiments, the spherical protrusion 134c is movably secured within the reciprocal cavity 136b using one or more pins, or another like fixation mechanism. The one or more pins may pass through the outer passage 109b at the distal end 130b of the middle core segment 110b and the inner passage 111c defined within the spherical protrusion 134c at the proximal end 132c of the bottom core segment 110c. The one or more pins may be present in addition to, or in the alternative to, the snap-fit of the spherical protrusion 134c in the reciprocal cavity 136b. The one or more pins may be present in addition to, or in the alternative to, the snap-fit of the spherical protrusion 134c within the reciprocal cavity 136b.

[0072] The distal end of 130c of the bottom core segment 110c may be flat and, when the ankle implant 10 is assembled, is adjacent to the top surface 52 of the tibial tray 50. The bottom core segment 110 may also include one or more openings 113 which may be useful for gripping1653545767.2the core 108 during insertion, adjusting the fit of the core 108 within the shell 102, and or accessing the threaded site 118 within the core 108.

[0073] The reciprocal cavities 136a, 136b may be at least partially defined by a cutaway 138a, 138b that, when the spherical protrusion 134b, 134c articulates within the cavity 136a, 136b, facilitates bending of the adjacent core segments 110 relative to one another. For example, the shape, size, and angle of the cutaway may dictate the direction in which the respective joint is able to bend and the extent to which the joint is able to bend.

[0074] In embodiments, first referring to the first joint 112a, the cutaway 138a defines a cutaway surface 139a which extends upwardly at a less than 90° angle from the bottom surface 137a of the distal end 130a of the top core segment 110a. When the core 108 is in the straight configuration, as shown in FIG. 4A, the bottom surface 137a is in a plane perpendicular to the longitudinal axis (LA) of the stem 100 and abuts a top surface 135b at the proximal end 132b of the middle core segment 110b surrounding the spherical protrusion 134b. As the first joint 112a bends, the bottom surface 137a of the top core segment 110a distances from the top surface 135b of the middle core segment 110b. In the fully bent configuration, such as that shown in FIG. 6C, the cutaway surface 139a abuts the top surface 135b of the middle shell segment 110b. In this way, the first joint 112a is only permitted to bend in the direction of the cutaway 138a, and the angle of the cutaway 138a relative to the plane perpendicular to the longitudinal axis (LA) of the stem 100 dictates the extent to which the first joint 112a is permitted to bend.

[0075] Similarly, referring now to the second joint 112b, the cutaway 138b defines a cutaway surface 139b which extends upwardly at a less than 90° angle from the bottom surface 137b of the distal end 130b of the middle core segment 110b. When the shell 100 is in the straight configuration, the bottom surface 137b is in a plane perpendicular to the longitudinal axis (LA) of the stem 100 and abuts a top surface 135c at the proximal end 122c of the bottom shell segment 104c. As the second joint 112b bends, the bottom surface 137b of the middle core segment 110b distances from the top surface 135c of the bottom core segment 110c. In the fully bent configuration, the cutaway surface 139b abuts the top surface 135c of the bottom core segment 110c. In this way, the second joint 112b is only permitted to bend in the direction of the cutaway 138b, and the angle of the cutaway 138b relative to the plane perpendicular to the longitudinal axis (LA) of the stem 100 dictates the extent to which the second joint 112b is permitted to bend.1753545767.2

[0076] The cutaways 138a, 138b may be any shape and / or size so as to provide the core joints 112a, 112b with the appropriate range of motion for the desired bending of the inner core 108. In preferred embodiments, the cutaways 138a, 138b are positioned so that each joint 112a, 112b is only able to bend in one direction and to a degree that is preferred for insertion of the inner core 108 along the sagittal plane. In this preferred embodiment, the cutaways 138a, 138b are aligned on a single side of the inner core 108 so that each core joint 112a, 112b bends in the same direction. In other embodiments, the cutaways 138a, 138b may be positioned so that the joints 112a, 112b can bend in multiple directions. In these other embodiments, the cutaways 138a, 138b may not be aligned on a single side of the core 108, thereby enabling the shell core 108 to bend in a different direction at each joint 112.

[0077] The stem system 100 as described herein may be made of any material suitable for use in the manufacturing of medical devices, particularly joint replacement implants. These materials may include, but are not limited to, bio-compatible metals (e.g., titanium and titanium alloys, cobalt chrome, etc.) and polymers (e.g., polyether ether ketone (PEEK), carbon reinforced PEEK, etc.). For example, the shell 102 and the core 108 may each be made of titanium, alone or in combination with one or more additional materials. In some embodiments, the shell 102 is made of titanium while the core 108 is made of PEEK. In other embodiments, the shell 102 is made of PEEK while the core 108 is made of titanium. According to preferred embodiments, the shell 102 and the core 108 are made solely of titanium. In some embodiments, the shell 102 has a porous structure to facilitate bone ingrowth. In embodiments, the shell 102 and / or the core 108 may be coated with one or more surface treatments. For example, the shell 102 may be coated with a porous coating to facilitate bone ingrowth. However, any suitable coating for improving bone ingrowth, adhesion, implant stability, biocompatibility, etc. may be applied to the shell 102 and or the core 108. In embodiments, a method 200 for inserting the stem portion of a total ankle replacement implant, as shown in FIGS. 5-6, is provided, using the stem system 100 described with respect to FIGS. 1-4B.

[0078] In embodiments, the method 200 includes preparing the patient’s ankle joint (210) for insertion of a total ankle replacement implant. Preparation of the ankle joint may include forming a cavity within the patient’s tibia (T) (i.e., forming a tibial canal) sized and shaped to receive the stem system 100. The tibial canal may be formed using one or more cutting implements (e.g., a reamer) to match the dimensions of the stem system 100. Methods of preparing the ankle joint1853545767.2and instrumentation therefor are described in PCT / US2025 / 024590 and PCT / US2025 / 015410, each of which is hereby incorporated by reference in its entirety.

[0079] After the tibial canal is formed, the outer shell 102 is arranged for insertion (220) into the tibial canal (TC). The outer shell 102 may be bent (as shown in FIG. 6) to facilitate insertion of the outer shell 102 at a desired angle. For example, it is preferable to insert the stem system 100 from the side of the patient’s ankle in the sagittal plane, into the space between the tibia and the talus. To facilitate insertion in this manner, the outer shell 102 should be bent so that the outer shell 102 may be inserted in such a way that it is, at least initially, perpendicular to the tibial canal (TC). While this is the preferred method of inserting the outer shell 102, other shell 102 configurations for other angles of insertion may be possible.

[0080] Once the outer shell 102 is bent to an acceptable angle, it may be inserted into the patient’s tibial canal (230). As previously described, the outer shell 102 may be bent at any angle but is preferably bent in a manner that facilitates insertion along the sagittal plane. As the shell 102 is advanced into the patient’s tibial canal (TC), the joints 106 will begin to straighten so that the shell 102 begins to take on the shape of the tibial canal (TC). Once the shell 102 has been completed advanced into the tibial canal (TC), the segments 104 and joints 106 will be aligned so that the outer shell 102 is straight (or substantially straight) within the tibial canal (TC) to take on the shape of the tibial canal (TC).

[0081] Following placement of the outer shell 102, the inner core 108 may be arranged for insertion (240) into the cavity 114 defined within the outer shell 102. The inner core 108 may be bent similarly to the outer shell 102 (as shown in FIG. 6) to facilitate insertion of the inner core 108 at a desired angle. In preferred embodiments, the inner core 108 is inserted at the same angle as the outer shell 102. However, in some embodiments, the inner core 108 and the outer shell 102 may be inserted at different angles, or the inner core 108 may be bent at different angles from the outer shell 102 to account for the different size, radius of curvature, etc. of the shell 102 and the core 108.

[0082] Once the inner core 108 is bent to an acceptable angle, it may be inserted into the cavity 114 of the outer shell 102 (250), which has already been placed within the patient’s tibial canal. As previously described, the inner core 108 may be bent at any angle but preferably is bent at the same or a similar angle to that of the outer shell 102. As the inner core is advanced into the cavity 114 defined within the outer shell 102, the joints 112 will begin to straighten so1953545767.2that the core 108 begins to take the shape of the cavity 114. Once the core 108 has been completely advanced into the cavity 114, the segments 110 and joints 112 will be aligned so that the inner core 108 is straight (or substantially straight) within the cavity 114 of the outer core 102.

[0083] In embodiments, the inner core 108 is sized and shaped to have a friction or interference fit within the cavity 114 of the outer shell 102, so that the inner core 108 is secure within the outer shell 102 upon insertion without any additional fixation means. The joints 106 of the outer shell 102 may also be offset from the joints 112 of the inner core 108, such that when the inner core 108 is inserted into the outer shell 102, the entire stem system 100 (i.e., the outer shell 102 and the inner core 108) are fixed in a straight (or substantially straight) configuration such that neither the outer shell 102 nor the inner core 108 is cable of flexing or bending about the joints 106, 112.

[0084] Finally, the tibial tray 50 may be secured to the stem system 100 (260). In embodiments, the tibial tray 50 is attached to the stem system 100 by inserting the mating protrusion 56 of the tibial tray 50 into the gap 116 in the cavity 114 of the outer shell 102 below the inner core 108. As described with respect to FIG. 2, the mating protrusion 56 may form a friction or interference fit within the cavity 114 to secure the tibial tray 50 to the stem system 100, without the need for additional fixation components (although these components may be present in some embodiments).

[0085] The partially assembled implant 10, after being inserted into a patient, is shown in FIG. 7. As shown in FIG. 7, once implanted, the stem system 100 is positioned within the tibia (T) at a distal end (DT) thereof superior to the talus (TL). The stem system 100 is also positioned within the tibia along the coronal axis (CA), which evenly distributes the load across the stem system 100 and improves the longevity of the ankle replacement implant.

[0086] Having thus described the present systems and methods in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description of the invention, could be made without altering the concepts and principles embodied therein.

[0087] It is also to be appreciated that numerous embodiments incorporating only part of the embodiments discussed herein are possible which do not alter, with respect to those parts, the concepts and principles embodied therein.2053545767.2

[0088] The present embodiments and optional configurations are therefore to be considered in all respects as exemplary and / or illustrative and not restrictive, the scope of the systems and methods being indicated by the appended claims rather than by the foregoing description, and all alternate embodiments and changes to these embodiments will come within the meaning and range of equivalency of said claims are therefore to be embraced therein.EMBODIMENTS

[0089] Some embodiments of the present disclosure can be described in view of one or more of the following:

[0090] Embodiment 1. A stem system for an ankle replacement implant comprising an outer shell comprising one or more shell joints, and an inner core comprising one or more core joints, wherein the inner core is configured to be received within a cavity defined within the outer shell, and wherein when the inner core is disposed with in the outer core, the shell joints and the core joints are vertically offset about a longitudinal axis of the stem system.

[0091] Embodiment 2. The stem system of Embodiment 1, wherein the outer shell comprises a plurality of shell segments, wherein each of the one or more shell joints is disposed between each adjacent pair of shell segments.

[0092] Embodiment 3. The stem system of Embodiment 1 or 2, wherein each of the one or more shell joints are ball-in-socket joints.

[0093] Embodiment 4. The stem system of any of Embodiments 1 to 3, wherein the one or more shell joints are configured to bend with a limited range of motion in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint.

[0094] Embodiment 5. The stem system of any of Embodiments 1 to 4, wherein the outer shell comprises three shell segments and two shell joints.

[0095] Embodiment 6. The stem system of any of Embodiments 1 to 5, wherein the inner core comprises a plurality of core segments, wherein each of the one or more core joints is disposed between each adjacent pair of shell segments.

[0096] Embodiment 7. The stem system of any of Embodiments 1 to 6, wherein each of the one or more core joints are ball-in-socket joints.

[0097] Embodiment 8. The stem system of any of Embodiments 1 to 7, wherein the one or more core joints are configured to bend with a limited range of motion in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint.2153545767.2

[0098] Embodiment 9. The stem system of any of Embodiments 1 to 8, wherein the inner core comprises three core segments and two core joints.

[0099] Embodiment 10. The stem system of Embodiments 1 to 9, wherein the inner core is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.

[0100] Embodiment 11. The stem system of Embodiments 1 to 10, wherein the offset between the shell joints and the core joints is effective to rigidize the stem system.

[0101] Embodiment 12. An ankle replacement implant comprising a stem system comprising an outer shell comprising a plurality of shell segments and one or more shell joints disposed between each adjacent pair of shell segments, and an inner core comprising a plurality of core segments and one or more core joints disposed between each adjacent pair of core segments, wherein the inner core is configured to be received within a cavity of the outer shell, and wherein, when the inner core disposed within the cavity of the outer shell, the stem system is rigidized.

[0102] Embodiment 13. The ankle replacement implant of Embodiment 12, further comprising a tibial tray.

[0103] Embodiment 14. The ankle replacement implant of Embodiment 12 or 13, wherein the tibial tray comprises a mating protrusion extending from a top surface thereof, the mating protrusion being configured to attach the tibial tray to the stem system.

[0104] Embodiment 15. The ankle replacement implant of any of Embodiments 12 to 14, wherein the mating protrusion is received within the cavity of the outer shell and is configured to attach the tibial tray to the outer shell using a friction fit, a press fit, or a tapered fit.

[0105] Embodiment 16. The ankle replacement implant of any of Embodiments 12 to 15, wherein each of the one of more shell joints are ball-in-socket joints.

[0106] Embodiment 17. The ankle replacement implant of any of Embodiments 12 to 16, wherein the one or more shell joints are configured to bend with a limited range of motion in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint.

[0107] Embodiment 18. The ankle replacement implant of any of Embodiments 12 to 17, wherein the outer shell comprises three shell segments and two shell joints.

[0108] Embodiment 19. The ankle replacement implant of any of Embodiments 12 to 18, wherein each of the one or more core joints are ball-in-socket joints.2253545767.2

[0109] Embodiment 20. The ankle replacement implant of any of Embodiments 12 to 19, wherein the one or more core joints are configured to bend with a limited range of motion in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint.

[0110] Embodiment 2E The ankle replacement implant of any of Embodiments 12 to 20, wherein the inner core comprises three core segments and two core joints.

[0111] Embodiment 22. The ankle replacement implant of any of Embodiments 12 to 21, wherein the inner core is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.

[0112] Embodiment 23, the ankle replacement implant of any of Embodiments 12 to 22, wherein when the inner core is disposed with in the outer core, the shell joints and the core joints are vertically offset about a longitudinal axis of the stem system, the vertical offset between the shell joints and the core joints being effective to rigidize the stem system.

[0113] Embodiment 24. A method of implanting a stem system for total ankle replacement implant comprising inserting an outer shell into a tibial canal of a patient, and inserting an inner core into a cavity defined within the outer shell, wherein the stem system has a unitary construction when the inner core is inserted into the cavity of the outer shell, and wherein each of the outer shell and the inner core are flexible, but the stem system becomes rigid when the inner core is inserted into the cavity of the outer shell.

[0114] Embodiment 25. The method of Embodiment 24, wherein the outer shell comprises a plurality of shell segments and one or more shell joints connecting each adjacent pair of shell segments.

[0115] Embodiment 26. The method of Embodiment 24 or 25, wherein the plurality of shell segments and the one or more shell joints enable the flexibility of the outer shell.

[0116] Embodiment 27. The method of any of Embodiments 24 to 26, wherein the outer shell is configured to bend at each of the one or more shell joints with a limited range of motion and in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint.

[0117] Embodiment 28. The method of any of Embodiments 24 to 27, wherein the inner core comprises a plurality of core segments and one or more core joints connecting each adjacent pair of core segments.2353545767.2

[0118] Embodiment 29. The method of any of Embodiments 24 to 28, wherein the plurality of core segments and the one or more core joints enable the flexibility of the inner core.

[0119] Embodiment 30. The method of any of Embodiments 24 to 29, wherein the inner core is configured to bend at each of the one or more core joints with a limited range of motion and in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint.

[0120] Embodiment 31. The method of any of Embodiments 24 to 30, wherein the outer shell comprises one or more shell joints and the inner core comprises one or more core joints, and wherein when the inner core is disposed with in the outer core, the shell joints and the core joints are vertically offset about a longitudinal axis of the stem system, the vertical offset between the shell joints and the core joints being effective to rigidize the stem system.

[0121] Embodiment 32. The method of any of Embodiments 24 to 31, wherein the inner core is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.

[0122] Embodiment 33. The method of any of Embodiments 24 to 32, further comprising attaching a tibial tray to the stem system.

[0123] Embodiment 34. The method of any of Embodiments 24 to 33, wherein the tibial tray comprises a mating protrusion configured to be received within the cavity of the outer shell.

[0124] Embodiment 35. The method of any of Embodiments 24 to 24, wherein the mating protrusion is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.2453545767.2

Claims

CLAIMSThat which is claimed is:

1. A stem system for an ankle replacement implant comprising: an outer shell comprising one or more shell joints; and an inner core comprising one or more core joints, wherein the inner core is configured to be received within a cavity defined within the outer shell; and wherein when the inner core is disposed with in the outer core, the shell joints and the core joints are offset about a longitudinal axis of the stem system.

2. The stem system of claim 1, wherein the outer shell comprises a plurality of shell segments, wherein each of the one or more shell joints is disposed between each adjacent pair of shell segments.

3. The stem system of claim 1, wherein each of the one or more shell joints are ball-in- socket joints.

4. The stem system of claim 3, wherein the one or more shell joints are configured to bend with a limited range of motion in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint.

5. The stem system of claim 2, wherein the outer shell comprises three shell segments and two shell joints.

6. The stem system of claim 1, wherein the inner core comprises a plurality of core segments, wherein each of the one or more core joints is disposed between each adjacent pair of shell segments.

7. The stem system of claim 1, wherein each of the one or more core joints are ball-in- socket joints.2553545767.

28. The stem system of claim 7, wherein the one or more core joints are configured to bend with a limited range of motion in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint.

9. The stem system of claim 6, wherein the inner core comprises three core segments and two core joints.

10. The stem system of claim 1, wherein the inner core is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.

11. The stem system of claim 1, wherein the vertical offset between the shell joints and the core joints is effective to rigidize the stem system.

12. An ankle replacement implant comprising: a stem system comprising: an outer shell comprising a plurality of shell segments and one or more shell joints disposed between each adjacent pair of shell segments; and an inner core comprising a plurality of core segments and one or more core joints disposed between each adjacent pair of core segments, wherein the inner core is configured to be received within a cavity of the outer shell; and wherein, when the inner core disposed within the cavity of the outer shell, the stem system is rigidized.

13. The ankle replacement implant of claim 12, further comprising a tibial tray.

14. The ankle replacement implant of claim 13, wherein the tibial tray comprises a mating protrusion extending from a top surface thereof, the mating protrusion being configured to attach the tibial tray to the stem system.2653545767.

215. The ankle replacement implant of claim 14, wherein the mating protrusion is received within the cavity of the outer shell and is configured to attach the tibial tray to the outer shell using a friction fit, a press fit, or a tapered fit.

16. The ankle replacement implant of claim 12, wherein each of the one of more shell joints are ball-in-socket joints.

17. The ankle replacement implant of claim 16, wherein the one or more shell joints are configured to bend with a limited range of motion in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint.

18. The ankle replacement implant of claim 12, wherein the outer shell comprises three shell segments and two shell joints.

19. The ankle replacement implant of claim 12, wherein each of the one or more core joints are ball-in-socket joints.20 The ankle replacement implant of claim 19, wherein the one or more core joints are configured to bend with a limited range of motion in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint.

21. The ankle replacement implant of claim 12, wherein the inner core comprises three core segments and two core joints.

22. The ankle replacement implant of claim 12, wherein the inner core is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.

23. The ankle replacement implant of claim 12, wherein when the inner core is disposed with in the outer core, the shell joints and the core joints are vertically offset about a longitudinal axis of the stem system, the vertical offset between the shell joints and the core joints being effective to rigidize the stem system.2753545767.

224. A method of implanting a stem system for total ankle replacement implant comprising: inserting an outer shell into a tibial canal of a patient; and inserting an inner core into a cavity defined within the outer shell, wherein the stem system has a unitary construction when the inner core is inserted into the cavity of the outer shell; and wherein each of the outer shell and the inner core are flexible, but the stem system becomes rigid when the inner core is inserted into the cavity of the outer shell.

25. The method of claim 24, wherein the outer shell comprises a plurality of shell segments and one or more shell joints connecting each adjacent pair of shell segments.

26. The method of claim 25, wherein the plurality of shell segments and the one or more shell joints enable the flexibility of the outer shell.

27. The method of claim 25, wherein the outer shell is configured to bend at each of the one or more shell joints with a limited range of motion and in a single direction to facilitate insertion of the outer shell from a side of the patient’s ankle joint.

28. The method of claim 24, wherein the inner core comprises a plurality of core segments and one or more core joints connecting each adjacent pair of core segments.

29. The method of claim 28, wherein the plurality of core segments and the one or more core joints enable the flexibility of the inner core.

30. The method of claim 28, wherein the inner core is configured to bend at each of the one or more core joints with a limited range of motion and in a single direction to facilitate insertion of the inner core from a side of the patient’s ankle joint.2853545767.231 . The method of claim 24, wherein the outer shell comprises one or more shell joints and the inner core comprises one or more core joints, and wherein when the inner core is disposed with in the outer core, the shell joints and the core joints are vertically offset about a longitudinal axis of the stem system, the offset between the shell joints and the core joints being effective to rigidize the stem system.

32. The method of claim 24, wherein the inner core is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.

33. The method of claim 24, further comprising attaching a tibial tray to the stem system.

34. The method of claim 33, wherein the tibial tray comprises a mating protrusion configured to be received within the cavity of the outer shell.

35. The method of claim 34, wherein the mating protrusion is secured within the cavity of the outer shell using a friction fit, a press fit, or a tapered fit.2953545767.2

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